I may be mistaken, but I don't think Synth is even in Bretonia, as Cambridge is providing enough non-paste food. Plus Planet Gaia doesn't need terraforming, as it's already good to go, other than all the explodings and Cambridge University stuff. The one rumors are about how the Gaians are dumb for not letting them expand to there.
That said, there seems to be a lot of variety in how hardcore or otherwise the Gaians are. At the very least, working with the KNF should be because of convenience only, but if you're getting assistance, why rock the boat?
Isn't that the same idea as the Mollys and Bretonia? The Mollys want the Brets out of Dublin, but if Kusari conquers it all, they're no better off. But if they help out, it could further their claims, right?
As a further thought with the Gaians and Mollys, I think the hostile side of neutral makes more sense than full blown enemies.